Interpretive Summary: In this paper, we report the results of our molecular mapping research focusing on identifying quantitative trait loci (QTL) in sweetpotato roots for dry matter, starch and ß-carotene content, and yield. This research provides an understanding of the inheritance of complex traits in sweetpotato, and serves as an initial step toward the identification and location of genes involved in the expression of these economically important traits in this crop. Furthermore, the research results are useful in the implementation of genetic marker-assisted selection and mapping strategies to facilitate the worldwide breeding efforts in improving the yield and nutritional values of sweetpotatoes.

Technical Abstract:
Development of orange-fleshed sweetpotatoes (OFSP) is essential for the improvement of the food supply and nutritional status of millions of people in developing countries, particularly in sub Saharan Africa. However, sweetpotato [Ipomoea batatas (L.) Lam] breeding is challenging due to its genetic complexity and marker-assisted breeding tools are needed to facilitate crop improvement. We identified quantitative trait loci (QTL) for dry-matter, starch, and ß-carotene content, and yield in a hexaploid sweetpotato mapping population derived from a cross between ‘Tanzania’, a white-fleshed, high dry matter African landrace, and ‘Beauregard’, an orange-fleshed, low dry matter sweetpotato cultivar popular in U.S. Two parental maps were constructed using a population of 240 clones. Strong correlations were observed between starch and dry-matter content (r>0.8, P<0.0001 in the storage roots, while moderate correlations (r=-0.6, P<0.0001) were observed for ß-carotene and starch content. In both parental maps, QTL analysis revealed the presence of 13 QTL for storage root dry-matter content, 12 QTL for starch content, 8 QTL for ß-carotene content, and 18 QTL for yield. Multiple QTL regression models developed for segregation of alleles in each parent explained 15-24% of the variation in dry matter content, 17-30% of the starch content, 17-35% of ß-carotene content, and 12-30% of the variation in yield. To the best of our knowledge, this research presents the only QTL mapping study published to date for dry-matter, starch, ß-carotene content and yield in sweetpotato. This work improves our understanding of the inheritance of these important traits in sweetpotato, and represents a first step toward the long-term goal of developing marker-assisted breeding tools to facilitate sweetpotato breeding efforts.